Laminated ski and method of making same



NOV- 23, 1954 G. B. RHEINFRANK, JR 2,695,178

LAMINTED SKI AND METHOD OF MAKING SAME Filed June 15, 195o INVENToR. w65006.? e H//f//vf/fW/vAv/e WG 7 M @W United States Patent LAMINATED SKIAND METHOD 0F MAKING SAME George B. Rheinfrank, Jr., Perrysburg, OhioApplication June 15, 1950, Serial No. 168,193

2 Claims. (Cl. 280-11.13)

This invention relates to articles composed of dissimilar materials andmore especially to an improved type of ski and method or process offorming same.

It has been conventional practice for many years to fashion skis fromwood. By reason of its comparatively low density and low heatconductivity coupled with the factor of desirable resilience, wood hasbeen the most used material for manufacturing skis. Wooden skis havecertain inherent disadvantages and require considerable care to keepthem in conditionv for best use. They are subject to warpage andnonuniform shrinkage resulting from changes in moisture content andtemperature fluctuations, and are unstable in that they tend, to becomedistorted and lose their shape. Furthermore, it is practicallyimpossible to accurately match the individual skis because of thevariations in the characteristics of wood. Another disadvantage is thata wooden ski is not endowed with desirable high strength characteristicsand in use is often subjected to stresses approaching its ultimatestrength.

It has been proposed to fashion skis of composite materials utilizing acore of low density material such as wood covered with relatively highstrength fibrous material impregnated and bonded to the core through themedium of a suitable resin or plastic. This provides a stressed skinconstruction having several advantages over a wooden ski in that animproved wearing face is provided, the reinforced plastic or resin skin,having high strength characteristics, satisfactorily carries the bendingor exing loads while the core assists in stabilizing the faces of theski. Skis of this character have been made embodying a core of woodgenerally rectangular in cross section covered with a plurality oflayers of fibrous material impregnated or coated with resin. While skisof this character attained numerous advantages as compared with a woodenski, there are certain attendant disadvantages. For example, if thesides of the skis are crossed during use, extensive wear may beencountered on the top edge of one ski near the tip through itsengagement with the edge of the other ski and in some instances the skinlayer may be worn through or punctured. Such condition exposes the coreto the absorption of moisture which causes separation or delamination ofthe materials rendering the ski unfit for use. In fabricating a ski ofthis nature, the core must be accurately fitted on the edges to securethe proper distribution of skin thickness adjacent the edges. Moreover,a low density core such as balsa or poplar is relatively porous and isreadily subject to shrinking or swelling in moisture conditions whichcause its dimension to be modified. As the mold or die in which the skiis formed is of iixed dimension, a shrinkage of the core results inimproper bonding of the covering, and a swelling of the core necessarilyresults in a nonuniform covering. Furthermore, it has been diicult towrap the fabric plies around the core and at the same time avoid theformation of wrinkles or overlaps in the fabric when pressure is appliedduring the molding operation.

The present invention embraces the provision of an improved ski andmethod of producing the same which in a large measure minimizes orsubstantially eliminates these difficulties whereby skis of uniformcharacter may be produced economically.

An object of the invention resides in the provision of an improved skiconstruction embodying an edge formation which resists wear and greatlyprolongs the useful life of the ski.

Another object of this invention is to provide an immaterials. l,tto theface plies pf plywood, may preferably be formed of glass fiber inftheform of yarn, Woven cloth, or mat,

keithe use 2,695,178 Patented Nov. 23, 1954 lCe proved ski embodying astressed skin construction and having lateral edges formed of highdensity materials extending substantially beyond the edge of the core,said edges being fabricated of portions of the upper and lower surfacesof the facing or skin material combined with a suitable reinforcingmedium.

Another object of this invention is the provision of an improved skihaving a high strength, high modulus of elasticity facing material incombination with a low density core having the general contour of thefinished ski with the edge walls thereof beveled or canted to present agenerally trapezoidal shape in cross section.

Another object of the invention is to provide an improved ski havingfaces formed of high strength material bonded to a low density core theedge walls of which are contigurated in a manner whereby verticalpressure exerted on the ski during formation sets up a laterally actingcomponent of force in the direction of the sides causing the highstrength material adjacent the sides to establish a satisfactory bondand produce a completely formed edge in the mold.

A further object of the invention is to provide an improved ski wherebya high strength, high density material is employed as a primarystress-carrying medium suitably suported by a low density core materialsuch that the composite construction is of low average density endowedwith a relatively high strength-weight ratio, the ski having highdensity edges to adequately protect the core from crushing stressesshould the ski be jammed against other objects.

Still another object of this invention is the provision of high densitymaterial at the edges of the ski to which metal inserts may beintegrally molded therewith or secured to the ski after completion ofthe molding operation.

Still another object of the invention is to provide an improvedlaminated ski whereby a high strength facing material completelyembraces and is bonded to a low density core wherein a substantialportion of this material concentrated at the edge portions which aresubjected to the greatest wear.

Still another object of this invention is the provision of an improvedski having face layers formed of high strength materials bonded to a lowdensity core fashioned to a configuration so as to eliminate thenecessity of fitting the core accurately in the mold.

The improved construction, of particular use in the manufacture of skis,consists of a laminated structure the core of which is formed of agenerally cellular material having substantial shearV strength and theface plies of which are formed of fibers of great strength embedded in ahard adhesive. The adhesive may also be used to bond the face pliestothe core material. Generally cellular ma/terialszfpr the core materialinclude cellular cellulo'sea'cetate; baisa, poplar, or other varietiesof low density The faces of the laminated structure, similar gtie or incombination with fibers of other mteriwalwg/The fibers areemvlgeddeiinnand-fheld together by an adhesive that is capable'ldiiighsurface of the glass fibers and to the core material.

If the face plies are composed chiefly of glass fiber, hardenablesynthetic resins such as a polymerizable unsaturated polyester (i. e.,polymerizable unsaturated polyhydric alcohol-polycarboxylic acidpolyester, which is prepared by reaction of one or more polyhydricalcohols and one or more polybasic acids) or a polymerizable allyl ester(e. g., an ester or mixed ester of two alcohol molecules, eachconsisting of a molecule of allyl, crotyl, alphamethyl allyl, methallyl,beta-chloro allyl or beta-methyl crotyl alcohol, with a molecule of adibasic acid) or mixtures thereof are suitable for use to form the hardadhesive. If the fibers of the face plies consist largely of cellulosicmaterials, other hardenable resins such as phenolor urea-formaldehyde ormelamine-formaldehyde condensation products may be employed.

The fibers of great strength may be oriented in the face plies so that asubstantial number of fibers extend generally longitudinally ofthe.ski...or ,olb.e1 a1llg1s2llti to impart desired strength in bendingto the artic e. i

is also desirable in the construction of a ski that at least some (andin some types of construction all) of the fibers making up the faceplies extend across the faces either directly or diagonally and thusprovide considerable strength to resist torsional deiiection of the endsof the s 1.

Glass fiber, either in the form of yarn, cloth or mat, is particularlywell adapted for use as the surface layer of a ski because of itsunusual strength in tension, its resistance to abrasion and itsresistance to deterioration by water. Furthermore, the layer of glassfibers embedded in a hard resin adhesive has a low coefficient of heatconductivity so that the finished ski is comparable in this respect to aski "constructed entirely of wood.

The use of fibers embedded in a hard adhesive, and glass fibers inparticular, provides a finished article in which the resiliency andstrength characteristics may be precisely controlled. It is thuspossible to provide exactly matched skis or skis designed to particularspecifications as far as strength and resiliency are concerned.

Another advantage in the use of glass fibers embedded in a hard adhesiveis that the yield strength and the ultimate strength of the finishedarticle are nearly the same in magnitude and both are higher than thestrength obtainable in other suitable materials so that the articlewithstands normal use without danger of failure either in fracture orpermanent deformation. The high yield strength plus the permanency ofglass provides a finished ski that retains its camber, strength, anddamping characteristics without requiring special care.

Further objects and advantages are Within the scope of this inventionsuch as relate to the arrangement, operation and function of the relatedelements of the structure, to various details of construction and tocombinations of parts, elements per se, and to economies of manufactureand numerous other features as will be apparent from a consideration ofthe specification and drawing of a form of the invention, which may bepreferred, in which:

Figure 1 is a plan view illustrating a form of ski constructed accordingto the invention;

Figure 2 is a side elevational view of the ski construction;

Figure 3 is a transverse sectional view taken substantially on the line3-3 of Figure l;

Figure 4 is a transverse sectional view taken substantially on the line4 4 of Figure 1;

Figure 5 is a transverse sectional view taken substantially on the line5 5 of Figure l;

Figure 6 is a semidiagrammatic illustration showing the orientation ofthe core, face layers and edge reinforcing material prior to the moldingoperation;

Figure 7 is a sectional view illustrating a modified configuration ofcore structure;

Figure 8 is a transverse section of a mold construction suitable for usein forming the ski of my invention;

Figure 9 is a sectional view of a mold adapted to accommodate metalinserts or strips for integration with the ski during the moldingoperation, and

Figure l0 is a sectional view of the female section of a mold with thematerials of Figure 6 assembled therein preparatory to a moldingoperation.

These specific figures and the accompanying description are intended tomerely illustrate the invention and are not intended to imposelimitations upon the claims.

Referring to the accompanying drawings, an improved ski 1 constructedaccording to the invention, is similar in size and shape to aconventional ski. The length and width of the ski may be variedaccording to the preference of the user and the thickness may vary alongthe length of the ski so as to achieve as nearly as possible a uniformload distribution to the snow beneath the ski. The uniform loaddistribution is affected both by the resiliency of the ski and theamount of camber or bend that it has in its unloaded condition. Thus aski with a large amount of camber must be made relatively weak to allowit to straighten out under normal load while a ski having little cambermust be relatively much stronger to carry the same load when deiiectedto a straight condition.

The improved ski 1 is provided with customary fittings 2 and heel pad 3to fit the usual type of harness.

It will he noticed in Figure 2 that the thickness of the ski variesalong its length and is greatest at the center where the bending momentsare normally the greatest when the ski is in use. For an average ski thethickness of the core may vary from one-eighth of an inch at the toe toapproximately three-quarters of an inch at and slightly forward of theharness fittings 2 and then taper to approximately iive-sixteenths of aninch near the heel of the ski. These dimensions are illustrative onlyand may be varied to modify the characteristics of the ski. Thus thecore of a ski intended for a light-weight person is relatively thinnerthan a ski intended for a heavy person.

As particularly shown in Figures 3, 4 and 5, the sides or side walls ofthe core 4 are beveled or canted to provide adequate space between theedge of the core and the adjacent side wall of the mold to facilitatethe formation of high density sides formed by layers 6 and 7 of materialcomprising the upper and lower surfaces of the ski and additionalreinforcing material 8. It is pointed out that skis of conventional sizemade according to the invention are fashioned with the height of thehigh density edge portion approximately one-quarter of an inch in allsections of the ski as shown in Figures 3 and 4 with the exception ofthe foot plate section. At the foot plate section as shown in Figure 5the sides are substantially vertical to accommodate the ski binding orfitting 2. By forming the edge of the ski in this manner the weight ofthe ski is reduced to a minimum yet providing the ski with tough, densestrong edges throughout the length thereof. By beveling or canting thesides or side walls of the core in the manner shown in Figures 3, 4 and5, the core does not have to be accurately fitted in the mold as theedges of the ski are formed by portions of the facing material and thereinforcing material disposed adjacent the sides of the core. It will beapparent that by forming the core with slanting sides, sufficientpressure applied in a vertical direction upon the mold causes the skinmaterials to bond with the core as well as to completely form the edgesof the ski. The center core section 4 of the ski extends substantiallythe full length of the ski and is formed of material that is light inweight and has good shear strength properties. Balsa, Basswood andPoplar are found to be suitable for this purpose. The side walls of thecore may be of any delstied configuration to fulfill the purposes asherein set fo Figure 6 shows a general arrangement or orientation of thematerials making up the skin or face plies of the improved ski. Thecross section of the ski comprises the central core material 4, aplurality of layers 6 and 7 of the skin material respectively applied tothe upper and lower faces of the core material, and additional layers 8at the edges of the ski as a reinforcement therefor. The layers 6 and 7include a substantial number of longitudinally extending fibers eitherin the form of yarn, cords or longitudinal threads of cloth, or a mat offibers such as glass fibers in which many of the individual fibers areoriented along the length of the ski.

Prior to assembly or molding operations, the materials forming layers 6and 7 and edge reinforcement 8 may be coated or saturated with ahardenable resin, adhesive or plastic, the amount of the resin beingfrom 35% to by weight of the saturated or coated materials. The skinlayers, particularly the outermost one, may also include somelongitudinally extending abrasion resistant fibers to improve therunning surface of the ski. These fibers may be of rayon, cotton, fibersformed from linear fiber forming polyamides or other synthetic organicfibers.

Figure 8 illustrates a mold suitable for use in constructing theimproved ski. The mold is inclusive of a female member 1), the interiordimensions and contour of which conform to the lower surface and edgeformation of the finished ski. A male mold 11 is adapted to fit into theupper surface configuration of the ski. rfhe raised portions l5 and 16in the female mold 10 are for forming the rabbets or recesses along theedge of the ski to receive the metal strips 12 which may be of steel orother suitable metal or alloy. As shown in Figure 1l, it may be desirable to dispose the steel edge strips 12 in the female mold in lieuof the raised portions 15 and 16 and mold these strips integrally intothe skis. The strips 12 may be held to the ski body by means of screws14 or other securing means.

The procedure in constructing the ski, assuming that the skin layershave been preimpregnated or coated with resin, consists of disposing theouter layers 7 in the female mold 10. Next the core 4 is placed over theskin layers 7. The edge reinforcing material 8 is then laid adjacent thesides of the core and lastly the upper skin layers 6 comprising theupper surface of the ski are placed over the core. The male section 11of the mold is then brought into cooperative relation with the femalesection forcing the skin layers and edge reinforcement into intimatecontact with each other and with the core. The mold is then placed in asuitable press (not shown) and the entire assembly maintained atelevated temperature for a period of time sufiicient to harden or curethe resin.

It is sometimes desirable, particularly when custom building skisaccording to specified characteristics, that the characteristics of theski, such as its resilience and strength, may be varied without changingits outside dimensions. As long as the outside dimensions remainunchanged the molds used to hold the ski during the hardening of theresin may be used Without alteration. To satisfy this condition andstill provide selection of finished ski characteristics it is possibleto vary the number of layers of skin material in the face plies of theski as well as to vary orientation of the high-strength bers withrespect to the long axis of the ski. Thus, if one desires to increasethe strength and stiffness of' the ski a number of layers of fibershaving high strength such as the layers 6 and 7 are laid on the faces ofthe core material with the high-strength fibers extending longitudinallyof the ski. If it is desired to decrease the stiffness of the ski, thismay be accomplished without change in dimension by orienting thehigh-strength fibers diagonally on the ski some in one direction andsome in the other and at angles with respect to the center line of theski such that the resulting components of stress parallel to the axis ofthe ski strength characteristics.

The improved ski is representative of improved laminated articles thatmay be constructed according to the invention. By using glass fiber anda suitable hard adhesive it is possible to construct a replacement skithe,

provide the desired/ characteristics of which will exactly match thoseof the ski it is to replace.

Various substitutions of materials and numbers of layers of skinmaterial or substitutions in core material may be made without departingfrom the spirit and scope of the invention.

Having described the invention, I claim:

l. A ski comprisingl a core of low density material having its crosssection of substantially trapezoidal shape, layers of high density,resinous, fibrous material encompassing said core and bonded to saidcore, said layers including a first series bonded to the top and bottomportions of said core having its edges extending transversely beyond thelateral walls of said core and a second series parallel to said firstseries and bonded to the lateral walls of said core and to said firstseries, each of said layers having its fibrous material oriented in asingle direction.

2. A ski comprising a core of low ,density material having its crosssection of substantially trapezoidal shape, layers of high density,resinous, glass fibered material encompassing said core and bonded tosaid core, said layers including a first series bonded to the top andbottom portions of said core and having its edges extending transverselybeyond the lateral walls of said core and a second series parallel tosaid first series and bonded to the lateral walls of said core and tosaid first series, each of said layers having its glass fibered materialoriented in a single direction.

Mmlkeferences Cited in the file of this patent UNITED STATES PATENTSName Date 2,038,530 Anderson Apr. 28, 1936 2,213,903 Davidson Sept. 3,1940* 2,371,305 Marks Mar. 13, 1945- 2,414,125 Rheinfrank, Jr. Jan. 14,1947 2,454,719 J Scogland Nov. 23, 1948 2,470,227 Wheeler May 17, 1949"2,525,618 Pierce Oct. 10, 1950 FOREIGN PATENTS Number Country Date733,250 France July 4, 1932

